Modern buildings, using typical construction components such as reinforced concrete shear walls, structural steel braced frames, structural steel or reinforced concrete moment frames or combinations thereof, have low inherent damping properties which decrease with building height. Due to this low inherent damping, high-rise buildings, in particular, tend to be susceptible to excessive vibrations caused by dynamic loads. Excessive accelerations and torsional velocities can cause occupant discomfort, while excessive displacements can cause damage to non-structural and structural elements. For this reason it is advantageous to provide additional sources of damping to control these excessive vibrations and reduce the overall building response to dynamic loads. These dynamic loads can include both those resulting from wind loads and earthquake loads.
Currently available systems for controlling displacements, velocities and accelerations in such structures consist of passive systems such as supplemental dampers and vibration absorbers as well as active systems.
Passive supplemental dampers such as hysteretic, viscous and visco-elastic dampers are currently used in typical braced configurations and are activated under axial deformations. While this may be effective in adding damping to some structural configurations, where under this typical braced configuration the brace elements undergo significant axial deformations, they are less effective for other structural systems, such as structural systems commonly used in high rise buildings where the primary mode of lateral deformation does not cause sufficient axial deformation in typical bracing elements to effectively activate such dampers. In order to increase the deformations to an extent sufficient to activate the dampers, special configurations using toggle bracers or scissor braces to amplify the displacements have been used.
Vibration absorbers such as Tuned Mass Dampers (TMD) and Tuned Liquid Dampers (TLD) are also used to reduce the deflections, velocities and accelerations of such structures during wind loading. They typically consist of a mechanical vibrating system inserted on the top floor of buildings in order to maximize their effectiveness. This has the disadvantage of using up some of the most valuable real estate within the building in addition to being expensive to design and to build. They also act in a limited frequency range as they must be tuned to a single mode of vibration.
Active systems require an external power source, an actuating force and extensive hardware and software control systems. As a result, they are expensive to design and implement, and are susceptible to power outages or failure of the control system.
One solution to the above-identified problems with existing systems was proposed in PCT Application No. PCT/CA2006/000985 filed Jun. 16, 2006, entitled “Fork Configuration Dampers and Method of Using Same.” The system in that application presents a configuration for damping systems in buildings for interconnecting two elements of a structure that undergo relative movement with respect to each other. The damping system of the '985 application discloses a first set of plates fixed to a first generally vertically extending structural element provided for resisting lateral loads and a second set of plates fixed to a second generally vertically extending structural element provided for resisting lateral loads. The vertically extending structural elements may, for example, be walls, columns, frames or other vertical elements in a building. The first and second sets of plates each comprise a plurality of substantially parallel, spaced apart plate elements arranged such that the plate elements of the first set of plates are interdigitated with the plate elements of the second set of plates. A damping material is provided to couple the first set of plates to the second set of plates. In this manner, as the vertically extending structural elements undergo relative movement with respect to each other due to the application of lateral loads to the building, the first and second set of plates are displaced in a vertical shear movement and act to damp vibrations in the structure via the energy dissipating material resisting the displacement of the plates with respect to each other.
While this system provides significant improvement to prior damping systems, in the event of extreme wind loading and/or earthquake loading, deformations placed on the damping system may overload the system, causing an undesirable failure which may render the damper ineffective for subsequent cycles of loading. Accordingly, in the event of these extreme loading conditions which exceed the intended deformation state of the damping systems, a more ductile robust response would be advantageous. In addition following an extreme event it is difficult to repair or replace the damping system.